1. Field of the Invention
The present invention generally relates to power supplies for electronic devices, e.g., televisions, desktop computers, computer monitors, laptop computers, compact disc players, digital video disc players, and audio components such as receivers and tuners. The present invention specifically relates to a method and apparatus for controlling a soft switching of a switch of a flyback converter.
2. Description of the Related Art
A typical flyback converter includes a metal-oxide semiconductor field-effect transistor switch (xe2x80x9cMOSFET switchxe2x80x9d) that is selectively turned on and off in view of regulating an output voltage of the flyback converter. Specifically, the MOSFET switch is transitioned from an OFF state to an ON state at one of the valleys of a drain voltage of the MOSFET switch in view of an output power being transmitted by the flyback converter to a load. First valley switching occurs when the output power is within an upper end of a load range of the flyback converter. Referring to FIG. 1A, a gate voltage VG1 Of the MOSFET switch transitions from a voltage off level VOFF to a voltage on level VON when a first valley of a drain voltage VD1 is detected. An off-time period TOFF(HL) corresponds to an acceptable switching frequency for the flyback converter when the output power is within an upper end of the load range.
High order valley switching occurs when the output power is within an intermediate portion or a lower end of the load range of the flyback converter. Referring to FIG. 1B, a minimum off-time period TOFF(MIN) that extends beyond a first valley and a second valley of drain voltage VD1 is determined, and gate voltage VG1 transitions from voltage off level VOFF to voltage on level VON upon a first detection of a third valley of a drain voltage VD1 after an elapse of minimum off-time TOFF(MIN). An off-time period TOFF(IL/LL) corresponds to an acceptable switching frequency for the flyback converter when the output power is within the intermediate portion or the lower end of the load range.
The first valley switching as shown in FIG. 1A and the high order valley switching as shown in FIG. 1B is predicated upon a selection of a specific valley of drain voltage VD1 for transitioning gate voltage VG1 from voltage off level VOFF to voltage on level VON. However, this predication fails to recognize that two or more valleys of drain voltage VD1 may correspond to acceptable switching frequencies for drain voltage VD1. This predication also fails to incorporate other performance parameters of the flyback converter such as an efficient power operation of the flyback converter. The electronic industry is therefore striving to improve upon a control of a soft switching of the MOSFET switch.
The present invention relates to a control of a soft switching of a switch of a flyback converter. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
A first form of the present invention is a power supply comprising a flyback converter including a switch operable to be switched between an on state and an off state. The power supply further comprises a controller that is operable during a first switching time period to determine at least one soft switching frequency for transitioning the switch from the off state to the on state during a second switching time period. The second switching time period is subsequent to the first switching time period.
A second form of the present invention is a power supply comprising a flyback converter including a switch having a gate terminal, a drain terminal, and a source terminal. The power supply further comprises a controller electrically coupled to said gate terminal and said drain terminal. The controller is operable to provide a gate voltage to the gate terminal in response to a drain voltage at the drain terminal.
The foregoing forms and other forms, features and advantages of the present invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the present invention rather than limiting, the scope of the present invention being defined by the appended claims and equivalents thereof.